Add specification for seed fingerprints.

zip-0032.rst

@@ -379,6 +379,17 @@ A "Sprout address tag" is the first 4 bytes of the corresponding Sprout address
 intended for optimizing performance of address lookups, and MUST NOT be assumed to uniquely identify
 a particular address.
 
+Seed Fingerprints
+-----------------
+
+A "seed fingerprint" for the master seed *S* of a hierarchical deterministic wallet is given by:
+
+  BLAKE2b-256("Zcash_HD_Seed_FP", *S*)
+
+It MAY be used to uniquely identify a particular hierarchical deterministic wallet.
+
+No corresponding short tag is defined.
+
 
 Specification: Key Encodings
 ============================